February 13, 2009

In what must be the most touching and useful tribute to departed author Arthur C. Clarke ever attempted, a group of scientists authors are trying to dare time travel into existence. Sir Clarke famously stated that "when a [distinguished scientist] states that something is impossible, he is very probably wrong". And a lot of distinguished scientists just told LiveScience "Time travel is absolutely impossible".

The authors, including Charles Liu (author of "One Universe: At Home
In The Cosmos"), Brian Greene (of "The Elegant Universe") and Michio
Kaku ("Hyperspace") float a raft of objections to trans-temporal
travel. True to Clarke's statement, sometimes affectionately known as
"Clarke's Law", each objection seems more like reason to expect time
travel than rule it out. Professor Greene states that all time-travel
theories operate at the very boundaries of known physics, and are
therefore unlikely to work. As opposed to, say, the boundaries of our
understanding being where new discoveries are made. As Sir Clarke said
years ago: "The only way of discovering the limits of the possible is
to venture a little way past them into the impossible".

The other chief objection is the incomprehensible amounts of energy
required to punch a hole in spacetime, or stabilise a wormhole, or
engineer a double-cosmic-string-ring (yes, that's a real astrophysical
concept) capable of bending space hard enough to let us pop back to the
past. One point eighty-one jigawatts just isn't going to cut it here,
whatever "jigawatts" turn out to be, and most calculations show that
powering a time machine with a lightning strike would be like powering
a sixteen-wheeler with a bag of jelly babies. (So it seems Marty won't
be getting back to the future after all). Of course, the idea of
lighting up New York would have had you committed to a mental home in
the early eighteenth century. Pre-electricity, schemes were being
suggested to transport the increasing numbers of people to the scant
available heat and light in times of need.

Understand: the amount of energy we now take for granted was so
vast, so utterly unimaginable to people in the past that they were
preparing to restructure their whole society rather than even attempt
to generate it. Of course, this doesn't guarantee that we'll be able
to pop back and tell them. The false argument of past scientific
ignorance, the "didn't scientists used to think the world was flat"
gambit fails because we know so much more now. The key to progress is
our cumulative knowledge, developed and refined by generations of
researchers into a vast, accurate body of knowledge. We are far more
likely to be able to find what's possible than at any point in
history. What we know so far is probably right, and allows us to make
predictions about what might be possible.

But until we can explain absolutely everything, we should still steer clear of saying something is impossible.

Comments

Aside from the enormous amounts of energy there's also the problem that everything is in motion. The Earth is not where it was a day ago - it's a million miles further along in its orbit. The sun is traveling at 600,000 mph around the hub of the Milky Way which is heading towards the Great Attractor in Virgo. Most time travel devices depicted in SF wouldn't work - what is needed is a TARDIS.

A "Jigawatt" (sic) is nothing more, nor less, than a mispronunciation (by today's standards anyway) of what we would today call a "gigawatt," with a hard "g" as in "gigabyte," as in RAM and hard drive. Whereas a "gigabyte" is a thousand million bytes, a "gigawatt" is a thousand million watts (1000 megawatts).

The problem is that in 1985 when Back To The Future came out, the average person didn't know how to pronounce the prefix, "giga." It had existed for at least several centuries in the scientific world, but wasn't in anything like common use in everyday speech; I myself have been a science geek since I was about 3, and only learned to pronounce "giga," myself, when "gigabyte" came into common use. (And it still could have gone the other way, and we could have all been speaking about "jiggabytes" all these years.)

The producers/actors of Back To The Future had to take a stab at pronunciation, and chose a soft rather than hard G -- probably because the most familiar, similar-looking word in common use was "gigantic." Soft G, "jiggawatt."

Sorry for the many that in fact express the commonly used GigaWatt or Gigahertz (the frequency used by communicating with satellites and spacecrafts is in the Gigahertz region)...with this really strange wording.........WHO invented this ??

Chris is absolutely right...how do you write the Gigabytes of your DVD or Hard disk ??

Again why the gigawatt appears so extreme power ???

1,8 Gigawatt or 2,4 Gigawat is much much less than the power produced by a very normal power plant (you know those 'things' that after having produced electric power and after some high voltage lines and transformers reach your homes and PC).

GIgawatt can also be reached easily in a medium-large particle collider...it is said and sustained....by 'many'

A very powerfull radar ...could reach pulses of 1 Gigawatt....You may want to ask people at Arecibo...who knows what the answer would be.....

The magic gigawatt.....nothing magics....indeed a large power.

Yes it has been said that a large amount of energy would be needed for machines...or objets... to time travel.

Well is only this the issue ??? Is this the 'limitation ' for creating a wormhole ??

This appears to me 'NAIVE'.....as a minimum.

Gigawatt or ' Jigawatt ' as you and these guys prefer,
does NOT constitute any Physics limit..

Sorry but the problems of 'wormholes creation' ...are much more complicated...as You and them may want to learn at the proper NASA site (i do not bother you with the usual www......citation)

I agree with the actual difficulty for creating a wormhole...BUT....BUT as said at other articles....we are here to discover new things and technolgies...and Physics principles and validate them...NOT to state that this that appears impossible TODAY cannot be done tomorrow.

Disagree with the approach of the people that spoke in the article....aside from the disagreement with Gigawatt (this is the exact way in common Physics and engineering )

The thing is that we know relativistic time travel forwards *is* possible, and it has been proven.

I personally don't believe that travel backwards is possible, but I do know that it is possible to slow us down relativistically, and therefore it may even be possible to suspend us completely relative to time in one place.

@claudio: That's not a definitive proof that time travel is not possible. It is a proof that nothing we may recognize as a tourist has discovered time travel yet, or has been detected traveling to recorded history. Bearing in mind the 'butterfly' effect there are very obvious reasons for this.

It is commonly understood that one must travel faster than the speed of light to go back in time. So far, everyone of Einstein's theories that has been proven one way or the other have been proven true. His theory of relativity states, inter alia, that as an objects speed increases, its mass also increases. As its mass increases, the energy required to accelerate it further also increases. The result is that as one gets close to the speed of light, the mass (and the energy required to accelerate it) will approach infinity.

The conclusion one must draw is that going back in time, if at all possible, will not be accomplished by going fast.

I do not think that being ignorant of something, such as the undiscovered reaches of physics, implies that a proposition such as time travel is any more or less probable. It is not a question of ruling it out altogether. It is whether or not time travel is so improbable as to put it realistically in the category of the nonexistent. Because we do not know that something can be ruled out empirically does not mean it is any more likely to be so than not. I also would propose that a hypothesis about something we know very little about is more likely to be wrong than accurate, although that does not rule it out and it may be correct in some ways more than others.

Sometimes watching scientists waste time indulging themselves with notions of what's scientifically im-possible instead of indulging in their curiosity and appetite for discovery - unlocking the improbable and obscure possibilities that transcend the limitations of human perception and the convoluting influence of scientific zeitgeist (as our most celebrated scientists have done in the past) - makes me feel like they're dragging me backwards in time along with them instead of expediting our progression forward, bringing us closer to the next epoch of human progress...

Curiosity and discovery are good, lead us to new testable ideas, and certainly give us warm fuzzy feelings. Time spent determining what is or is not impossible (or inaccurate) is essential to working science though, and certainly not wasted or indulged time.

remember that Marty McFly, though he violates the rules set forth by Doc Brown, was forbidden to have contact with anyone in 1955 (...forbidden to disclose that he was from the future - implied...) because - as Doc Brown explained to Marty with absurd appreciation for the mathematical consequences of such an event: He could inadvertently create a paradox capable of ripping the very fabric of the space-time continuum!

...Perhaps that's why we haven't met anyone from the future...

Another idea that just occurred to me:
Perhaps you, Carl Sagan and I are not (yet) critical to the future survival of all of mankind, thus we are only extras interacting in the background of the film, independent of the action, plot, and storyline of the film; independent of the interests of time-travelers with an agenda.

Trent quoted Sagan: "Where are the tourists from the future?" What if time travel to the past is actually possible? I don't know if this theory has already been suggested, but what if time travelers who go back in time end up going back into a different universe (like a parallel universe)? What if just the act of traveling back in time creates a parallel universe which happens to be the time traveler's destination (universe)? Maybe our universe just doesn't work that way with regard to the obvious paradoxes. All of this is assuming there exists a mulitverse, of course. Could very well answer Sagan's question. =)

Time travel will exist in the future, just not in the form that we know it. Forget being able to travel back in time. Not possible. Forget instantaneous time travel. Again, not possible.

We already have the technology to send someone "into the future" it's just when they get there, their body has aged along with them. The time travel I see us being able to create is a combination of chemically induced comas mixed with a form of anti-aging. It's the most feasible version of "time travel" in existence.

If you want to look seriously at the physical possibility of time travel, read David Toomey's "The New Time Traveler," WW Norton, 2007. He goes back to the first physicists around Einstein who conceived in the 1930s of time travel or the sending of messages through time -- starting with Willem van Stockum, Kurt Godel, and Frank Tipler. Impressive efforts have been made to visualize the mathematics of time travel.